The crystal structure of hexamethylenediamine dihydrochloride

Hexamethylenediamine dihydrochloride is isomorphous with the dihydrobromide (monoclinic, space group P2₁/c). Better crystals are available, and a detailed structure analysis is given with Fourier projections along two axes mutually at right angles, from which the co-ordinates of all the atoms are obtained with an accuracy of about ±0.04 A. In the chain molecule there is evidence of alternating long and slightly shorter bonds, but the variations are close to the experimental limits. The shorter N-Cl distances are of two types, averaging 3.11 and 3.24 A. The latter figure is close to the sum of the ionic radii, and the shorter type is probably accounted for by hydrogen bonding between the chlorine and nitrogen atoms. The compact grouping of the halogen ions in the lattice is illustrated in the diagram.